Abstract The blood-brain barrier is a term used to describe the unique properties of the blood vessels that vascularize the central nervous system. These blood vessels tightly regulate the movement of ions, molecules and cells between the blood and the brain, thus controlling the extracellular environment of the neural tissue. Despite the importance of the blood-brain barrier, very little is known about how this barrier regulates the neural environment to modulate complex behaviors. We have identified that the metabolic enzymes that generate and breakdown the monoamine neurotransmitters dopamine and serotonin are enriched in the endothelial cells of central nervous system blood vessels, suggesting that blood-brain barrier metabolism may regulate the levels of these monoamine neurotransmitters which are critical for many complex behaviors. In preliminary studies we have identified that deletion of these enzymes in endothelial cells leads to deficits in social interaction, and have further found evidence that these vascular enzymes act as a metabolic buffer to the transport of monoamine precursors. Interestingly, polymorphisms in the genes encoding each of these enzymes have been linked with autism risk and/or severity, however the site of action and mechanism by which they regulate autism-related behaviors is not known. Here we will test the hypothesis that blood-brain barrier metabolism regulates autism-related behaviors including social interaction. We will further examine the mechanism by which blood-brain barrier metabolism may regulate the levels of monoamine neurotransmitters within the central nervous system, and how this affects behavior. Our ultimate goal is to determine whether the blood-brain barrier is a therapeutic target to modulate behavior.